[KAFKA-2359] New consumer - partitions auto assigned only on poll

• Type: Bug
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Affects Version/s: 0.9.0.0
• Component/s: consumer
• Assignee: Unassigned
• Reporter: Stevo Slavić
• Created: 24/Jul/15 16:20
• Updated: 19/Jul/18 18:40

Description

In the new consumer I encountered unexpected behavior. After constructing KafkaConsumer instance with configured consumer rebalance callback handler, and subscribing to a topic with "consumer.subscribe(topic)", retrieving subscriptions would return empty set and callback handler would not get called (no partitions ever assigned or revoked), no matter how long instance was up.

Then I found by inspecting KafkaConsumer code that partition assignment will only be triggered on first poll, since pollOnce has:

// ensure we have partitions assigned if we expect to
if (subscriptions.partitionsAutoAssigned())
    coordinator.ensurePartitionAssignment();

I'm proposing to fix this by including same ensurePartitionAssignment fragment in KafkaConsumer.subscriptions accessor as well.